Open relationship vs breakup vs cheating

Going crazy here and need a bit of advice! I am a 31 year ol guy who has been in a relationship for nearly 9 years with a guy of similar age who is wonderful. We are engaged. We plan for a family. I see us growing old together and I love him deeply. We have worked at keeping our relationship going through a lot. We have not just walked away when things got difficult because we both believe things are worth saving if they can be saved. Now I'm wondering whether we are just too incompatible given that for him an open relationship would really fire up jealousy that would destroy him and our relationship.
My problem is that I am coming to understand about myself that I am a free spirit with desires and urges that are becoming increasingly hard to suppress. I was his first partner, he was not mine. We complement each other in that he keeps me grounded and I encourage him to spread his wings. We have talked about the fact that I like my sexual freedom and we've even messed around a bit with other guys. In recent times he has come to me and asked to explore being dominant with him and he likes me to make him wear a chain and be a bit aggressive sexually. When I do this he goes wild. He likes to be owned and gets a buzz out of the fact it's me owning him. Unfortunately I don't really like it. I find the idea of ownership and having someone serve me sexually does not turn me on. I cannot give him what I have found is his biggest turn-on. I am finding I cannot get hard for him and I'm avoiding sex.
In the meantime I am growing ever more tempted to cheat. I would never ever have said this a few years ago but now I feel stuck. He has said he never wants an open relationship. I am not a jealous person put he feels painful amounts of jealousy. I am finding myself seeking out sexual encounters but not going quite through with it to the point where it's become addictive. I feel this is deceitful but when I have tried to talk to him about my feelings and urges he just gets hurt and upset. For this reason I'm damned if I do and damned if I don't - he wants me to be happy and have what I need, I want the same for him. But what I want would make him unhappy and what he wants (ie me to never have sexual encounters without him) is making me unhappy. For about 5 long years I have repected his wishes and put his needs before my own. Now I am going stir crazy.
Don't get me wrong, we still do have sex and find each other attractive I also find it a massive turn on the thought of him playing with someone else. I would like him to find someone capable of giving him the dominance that I don't enjoy and for him to be comfortable in his skin sexually. I know however, that he has said he doesn't care what he does, he just can't cope with what I might be doing.
This has been an issue that keeps coming up and we never seem to get past. Every time it does come up it upsets him so much that I back down and stay unhappy. I don't want to end it with him. For me sex is just sex. I am not going to prioritise sex over 9 years of shared love and memories - which I guess is why I'm still with him. Who I am as a person is someone who needs to explore everything life has to offer - I love learning, travelling, seeing things from a different angle. I love to grow and develop as a person. I am absolutely not down for your conventional relationship straightjacket where I have to pretend I'm never gonna have sex with anyone else ever again. But at the same time I need a home with love and understanding where I can be at peace with who I am instead of feeling guilty and deceitful all the time.
I have in my life a wonderful man who understands me in so many ways and who I don't want to be without. So I guess my options are: a) Have a talk with him about open relationships again - and await the inevitable hurt and upset that causes for months on end before it goes back to how it always is. b) Break up and lose the love of my life, the future I dreamed of and be sexually and emotionally free but all alone in the world knowing that I found someone extremely right for me but blew it. c) cheat like a bastard because it's the easy way of him feeling happy by never knowing and me getting the sexual release I need (I do not like option c but if this goes on I know that I am not strong enough to resist temptation forever).

Writing this question has been like writing an essay but it's also felt cathartic in that I can at least ask the opinion of people who might understand rather than seek out the disapproval of all my friends who think we are some kind of perfect couple. I want us to be happy but I have put his needs first for many years at the cost of my own. I love him and don't want to lose him. Any advice is greatly appreciated. Thank you